Palmer



Oct. 25, 1960 w. PALMER Re. 24,891

CONTINUOUS WAVE NAVIGATION SYSTEM Original Filed Oct. 28, 1947 6Sheets-Sheet 1 osc/LbqToR fr y 1p-19.1.

HE/z/VE fffz ,L /TER l-ll I 3 2 f 4 ff asc/LLAMA' fz @ZISTR f2 f2 #Wnl/l//NsLow PALMER Hf/fm A TTORNE Y Oct; 25, 1960 w. PALMER Re. 24,891

CONTINUOUS wAvE NAVIGATION SYSTEM Original Filed 001'.. 28, 1947 6Sheets-Sheet 2 #fc5/VER I 56 PHHJE mTK Raf/vga gig-5M Z 2/ 7 um fg SENOI I I I I #uw T i? g Mom/410x f f3 RECEIVER @(5)- j 25 26 mm 27 #2.5mm(S-y) wifx-y) mm 26 71% W/X'Z) 535755? 211 2.9

1 I Y /Z) wf-T) OZ Wr X-z) L., F/L7 j #f my) Riff/YER 2 Y (1X1/)(2)"5mm" INVENTOR.

/NsLow PALMER Zw 5717EA' ATTORNEY Oct. 25, 1960 w. PALMER CONTINUOUSwAvx: NAvxGATIoN SYSTEM 6 Sheets-Sheet 3 Original Filed Oct. 28, 194'?fIL NQQQQ n Nk.,

Oct. 25, 1960 w. PALMER CONTINUOUS WAVE NAVIGATION SYSTEM Original FiledOct. 28, 194'? 6 Sheets-Sheet 4 .mk uuml m. MR EE VM mM P WH o L 5 N MWY B mm md wlww ATTORNEY Oct. 25, 1960 w. PALMER Re. 24,891

CONTINUOUS wAvE NAVIGATION SYSTEM INVENTOR. VV//VJL 0W PALME/e iwf/w.

A TTORNEY Oct. 25, 1960 w. PALMER Re. 24,891

' CONTINUOUS wAvE NAvIGA'rmN SYSTEM Original Filed Oct. 2B, 194'? 6Sheets-Sheet 6 o MPL/HER P//HSL' T0 BE MIARS'URED f4 NVENTOR. W//vsLowPALMER 4 TTORNEY United States Patent O 24,891 CONTINUOUS WAVENAVIGATION SYSTEM Winslow Palmer, West Hempstead, N.Y., assignor, by

mesne assignments, to Seismograph Service Corporation, Tulsa, Okla., acorporation of Delaware Original No. 2,611,127, dated Sept. 16, 1952,Ser.. No. 782,529, Oct. 28, 1947. Application for reissue July 9, 1953,Ser. No. 367,125

41 Claims. (Cl. 343-105) Matter enclosed in heavy brackets E appears inthe original patent but forms no part of this reissue specification;matter printed in italics indicates the additions made by reissue.

This invention relates to continuous wave radio position determiningsystems and more particularly to the elimination of cyclic ambiguity insuch systems.

Radio navigation systems of the hyperbolic type, such as loran arewell-known. In `these systems, a master and a slave station transmitpulses having a denite time relationship, and the difference of time ofreception of the pulses is measured at the receiving location therebyestablishing a hyperbo-lic locus of receiving positions relative to thelocation of the transmitter stations. Another combination oftransmitting stations is utilized to provide an intersecting hyperboliclocus of positions and thereby a navigational tix.

Continuous Wave hyperbolic radio navigation systems `are alsoWell-known. In this type of system, the continuous wave signals have Iadenite phase relationship at the transmitting locations and thedifference in phase at the receiving location is utilized to determinea. hyperbolic locus of positions relative to the transmittingloc-ations.

A serious diliiculty encountered with continuouswave systems is cyclicambiguity. It is relatively easy to measure a difference in phase ofless than one cycle but it is difficult to keep track of full cycle ofphase dierence. In practical operation, it is quite necessary to resolvethis cyclic ambiguit For example, at 2,000 kilocycles the Wavelength is150 meters, a 'distance which is rapidly traversed by a fast movingaircraft.

Several methods have been proposed for resolving the cyclic ambiguityand they are as follows:

(l) Start from a known point and keep a continuous record of the changeof position.

This method is practical and useful only for such purposes as surveyingor reconnaissance where a minimum of receiving equipment is advantageousand a continuous record is kept. lt is also useful for low velocitytravel such as marine navigation. In this method the calibratedinstrument is set at the known starting position and is operatedcontinuously and counts full cycle changes of phase. It is not suitableWhere the operation is not continuous, and it may not be used forintermittent operation or where there is a probability of interruptionof lthe use of the equipment.

(2) Limit the base lines between the transmitted locations to a halfWavelength.

This makes the total phase shift on going from one Station to another tobe but one full cycle so that the system is substantially unambiguous.However, the short base line seriously reduces the accuracy and area ofcoverage of the system.

In this invention, the ambiguity is resolved by utilizing two channelsslightly separated in frequency. The difference frequency between thechannels may be etectively utilized as a second system Whose wavelengthis long enough so that its phase shift is substantially unambigu- ICCous. This longer wavelength system is used as a medium reading toresolve ambiguity in the fine high frequency readings. A furtherextension of the non-ambiguous range is obtained by using synchronizedlow frequency modulation signals on the above-mentioned pair of carrierchannels in a manner that will be explained hereafter. These modulationfrequencies may be utilized `as.' a third coarse system having aWavelength long enough to resolve ambiguities in the medium system.

Accordingly, a principal object of the invention is to provide acontinuous wave radio navigation system without cyclic ambiguity.

Another object of the invention is to provide a oon- Itinuous Wave radiohyperbolic navigation System without cyclic ambiguity, which may beoperated intermittently.

Another object of the invention is to provide a continuous Wave, radionavigation system utilizing phase comparison of radio frequencies.

The invention also relates to the novel features or principles of theinstrument-edities described herein, whether or not such are used forthe stated objects, or in the stated elds or combinations, wherein Figs.l and 2 are diagrams illustrative of the principles of operation of theinvention;

Fig. 3 is a schematic diagram illustrative of a continuous wavehyperbolic navigation system;

Figs. 4, 5 and 6 are schematic black diagrams illustrative of continuous[waves] wave hyperbolic navigation system;

Fig. 7 is a schematic block diagram illustrative of a continuous [waves]wave hyperbolic navigation system, without cyclic ambiguity;

Figs, 8 and 8A are schematic block diagrams of a continuous [waves] wavehyperbolic navigation system, without cyclic ambiguity;

Fig. 9 is an embodiment of phase meter apparatus adapted for use in theinvention.

Figs. l0 and ll are vector diagrams illustrative of the operation of thephase meter of Fig. 9.

The operation of the system of this invention may best be understood byconsidering three basic principles, as follows:

PRINCIPLE I Given a transmitter at one location, radiating a Wave ea=esin 21rft (1) the wave at the receiver is then es=e sin 21rf (t-R/v) (2)where R is the distance from the transmitter to the receiver and v isthe propagation velocity of the Waves.

The wavelength (A) is given by Hence, the wave at the receiver lags theWave at the transmitter by an angle equal to 21rR/)t radians.

PRINCIPLE II therefore When two Waves are mixed and the heterodyne beatis extracted, if either of the component waves is shifted in'phasethrough a certain angle, the beat frequency Will shift in phase throughthe same angle.

This may be proved as follows:

Consider a system as shown in Fig. 1. It consists of two oscillators, 1and 2, generating different frequencies (f1.) and (f2). The wave fromoscillator 1 may be representedy by a` vector El as,- in Fig; 2. Thewave from oscilltor 2 may be considered to have the same frequency asthe wave'from oscillator 1 with an additional continuous'change in phaseat a rate equal to the diiference in frequency, or angular rate of21r(f1f2) radians per second. The wavemay be represented by the vectorFm which rotates continuously relative to vector F1, as indicated by thearrow. v

The angular position of; vector. F2 in addition to the Steady mtatgndueto thsffrefiuency d iierene, may be shifted an additional vamountkpb'y phase shifter 3 as indicated byy F2.

Tlczsumfof; the twcvcctors. F1 and F'z isv a vector whose magnitude maybe found by the Iw of COSines:

of the variations of the magnitude of the sum vector Fl-{TFZ due to therotation and shiftin phase of f'g relathe phase of `the heter-odyne beattive to fll' Therefore, q varies by they angle @exactly asthe phase ofFz varies bythe angle 95 relativeto F2 and F1.

PRINCIPLE III @modulated wave is. transmitted, the phase of` themodulation frequency wave, when demodulated at the reeeiver,V lagsthemodula-tion frequency wave at the transmitter, byan` angle equal tothe number of,wave lengths of the modulation frequency between thetransmitter and the receiver.`

Thismay beshown asV follows:

A modulated wave may be represented by the equation where.

fc is lthe carrier radliofrequency and fili'. is fllfsdilat'ifl'ff'saueacy At the receiver the waves will be retarded by the time oftravel (R/v) between: transmitter and receiver what@ R=,t1 1, distance,and

v=the velocity of propagation. Hansa .at th@ receiver.

e,=E,r11-m sin 21rfm(t-R/v)] sin frzfcu--Rf/v)` (7) A linear detector isnot affected by the phaseV of the carrier, hence, the -demodulated waveem will have the ffml.

clpv=rnEr` ,sinv [21rfmt-21rR/m] since mT-V/fm (9) Hence, the phase ,ofther, modulation frequency at the receiver will be retarded by 21rR/radians relative to the phase, of the ,modulation at the transmitter.

Referring to Fig..3 there is shown an embodiment of area they are),toserve, define lines of position as contours` of constantLph,ase,differene between the, beatr frequency',

waves directly'obtaned, :mining thesignalsyfrom Jthe from (a) by only afraction of a percent.

A-t station A there is a4 receiver 12 that receives both frequency (a)and frequency (b), beats them together, extracts the beat lfrequency(a-lb)` and modulates a third transmitter D, with the beat frequency, bymeans of modulator 13. Transmitters A and D are coupled together and, toantenna 1L by means of coupler 9.

The. receiver apparatus, at Sf, the position to be determined, containstwo radio frequency receivers. Receiver 16 receives frequencies (a)A and(b), beats them together and extracts the beat frequency Wave. Receiverllreceives the carrier frequency (d) and its modulation and extracts themodulation frequency. A phase detector 18 then measures the phase anglebetween the directly derived beat frequency, and the referencemodulation heat,l frequency..` The phase angle may be automaticallyindicated as follo-ws: the phase detector 18 generates a voltageproportionalto the cosine of the phase diierencg andfthis `voltage isvfed toservo 19 which turns the phase shifter. 20 in` such a manner as toreduce the phase difference to Calibrated indicator 21, which may be a,mechanical counter device, is geared to the- Shaft ofy servo 1,9, andthereby indicates continuously and automatically the phase difference.

The phase,v angle difference is a function of the positionoi thereceiver, and depends upon the diierence of thefdstanees fromthereceiver at S, to the transmitters `at A and B', respectively.Thiscan be shown as follsvs.

` The waves received` at arelresp'ectively en andl eb where e.,=e,l sin21ra(t-Ra/C) (10) and;

where R.,L andA Rb areA the` respective distances to A B Thephase .angle9 is measured :at the phase detector 18..`

between..themodulation. frequency and the beat frequency. and isobtained bytaking the difference of theV arguments in EquationslZ and15.

This @duss-S10 Equation 17 shows that the phase angle 0 between thebeaefrequeney andmodulationfrequency at the receiver dependsuupontheadiiferenceoffthe distances to thetwo transmitters plusy@constant thaV distance betweenLthetransmitters thatsfherphasetansis,isindependent@ thafrequeuiss S from transmitters A andvB.

t is determinedv yby .theE Itshould be notedA It is convenient toconvert the phase angle units to cycles and the distances towavelengths. When this is done, Equation 17 becomes Tb=M-l(Rs-Rb) (18)where Tb is in cycles of phase angle and Ra, Rb and M are in wavelengthsof frequency (b).

Since Ra and Rb are the distances of S from two fixed points, Fig. 3,Equation 18 represents a family of hyperbolae of constant phasedifference such as the line T, about the stations A and B as foci. Foreach value of Tb there is associated a unique hyperbola.

Fig. 4 illustrates a system for determining a navigational x. There arethree transmitters X, Y and Z, suitably separated, and the position tobe determined is designated as R. The transmitters Y and Z arecontinuous wave transmitters of ordinary crystal controlled stability,transmitting frequencies (y) and (z) respectively.

Located at transmitter X station, there is a receiver 40 which isadapted to receive the three frequencies (x), (y) and (z) and its outputis fed to detector 41. The detector 41 output is fed to filters 44 and45, their outputs being respectively difference frequencies (x-y) and(x-z). These diiference frequencies are fed to a fourth transmitter Wwhich transmits a carrier frequency (w) modulated with the two dierencefrequencies.

The receiving apparatus at R comprises two radio frequency amplifiers 21and 25. Amplifier 21 receives frequencies (x), (y) and (z). These threefrequencies are mixed in detector 22 and the desired beat frequency(1r-y), iS extracted by filter 24 and the desired beat frequency (X-z)is extracted by lter 23. The R.F. amplifier 25 receives (w) and itsmodulation frequencies (x-y) and (x-z) which are demodulated in detector26, and the modulation frequencies are separated in lters 27 and 28. Theseparately derived (x-y) frequencies are compared in phase meter 29 andseparately derived (1r-z) frequencies are compared in phase meter 30.The reading of each [phasemeter] phase meter determines one of theintersecting hyperbolic loci of positions one in range (y-x) and theother in range (y-z) thereby determining a navigational fix of theposition R relative to the location of the three transmitting stations.

The frequency (w) was suggested as the most direct means for obtainingthe reference modulation frequency (x-y) and (x-z) at the receiver. Thisfrequency (w) may be eliminated by providing that the beat frequenciesgenerated in mixers 44 and 45 be modulated upon transmitter X. To dothis the beat frequencies are divided by some small integer (p) in orderthat they may be later separated.

Fig. shows the equipment required at transmitter X location in order toaccomplish this result. In this case, the three frequencies (x), (y) and(z) are all received as before in receiver 40, mixed in detector 46, andthen fed to filters -47 and 48 which extract the proper beat frequencies(x-y) and (X-z). Each of these frequencies is divided by the samedivisor P in the frequency dividers 49 and 49', thus providing s? andaga which modulate transmitter X by means of modulator 50.

The cooperating equipment at the receiving location R is illustrated inFig. 6 and comprises a radio frequency amplifier 51 which receives thethree carrier frequencies (x), (y) and (z), plus the frequenciesmodulated upon the carrier frequency x, namely (X-lgy) and (X1-DZ) Allof these frequencies are mixed in detector 52, the output of which isconnected to four filters which extract the modulated beat frequencies,and the directly derived beat frequencies as follows; iilter `53extracts frequency (x-y), filter 54 extracts frequency (x-y) P filter 59extracts frequency (x--z) and filter 57 extracts frequency (X-z) P Thefrequency (x-y) P is fed from filter l54 to multiplier 55 whichmultiplies by the same factor P and thereby restores it to the originalfrequency (x-y). It is then fed to phase meter 56 in which it iscompared with the directly derived beat frequency (x-y) thereby givingan indication of the phase difference and determines a hyperbolic locusof position in the range (y-x). The frequency is fed from filter 57 tomultiplier 58 where it is multiplied by the same factor P and restoredto its original frequency (x-z). It is then fed to phase meter 60 whereit is compared with the directly derived frequency (x-z) obtained fromlter 59 and provides a reading of the phase difference, and determines ahyperbolic locus of position in the range (y-z) which intersects thefirst hyperbolic line of position.

All of the systems previously described are subject to cyclic ambiguityof phase shift. This problem is solved in the present invention byoperationg two systems similar to those already described, side by side,simultaneously, on dilferent frequencies. The two systems, in additionto their own indications, then cooperate to provide a third system basedupon a wavelength corresponding to the difference frequency between thetwo systems. The ambiguous regions of this longer system differencewavelength are fewer in number. This system difference concept may bevisualized by considering two rotating vectors of different frequencies.Assume they both start from a zero position at zero time and thereforethe higher frequency vector immediately starts to lead the lowerfrequency vector. At a certain time T the higher frequency vector willovertake the lower frequency vector, and this time T is equal to theperiod of their difference frequency. In other words, the differencefrequency has been phase shifted one full cycle in this time T. Bymeasuring a phase shift of this system difference frequency, of lessthan one full cycle, we may resolve cfyclic ambiguity in the phase shiftreadings of the higher frequencies. In addition the system may be soarranged that the modulation frequency of one [ssytem] system istransmitted in one station and the modulation frequency of the othersystem is transmitted in the other station. If now, the modulationfrequencies of the two system are synchronized, then the phasecomparison of the modulation frequencies at the receiving location willform a third system based upon wavelengths of the modulationfrequencies. This will be explained in detail hereinafter.

If the frequency difference between the systems is between 2% and 5% ofthe carrier frequencies and the modulation frequency is between 2% and5% of the difference frequency, then the resolution of the differencefrequency system will be less than the wavelength of the carrierfrequencies, and the resolution of the modulation frequency system willbe less than the wavelength of the difference frequency system, so thatthe entire `(at) by a few percent.

group of systems operating together have an accuracy prportinal fte thecarrier frequency system Yand an nnlbigds `fange proportional to "them'odulation Wavelength.

Fig. 7 is a block diagram of atwo station system which can define linesof position without cyclic ambiguity. A third station is required yfor anavigational fix but it has been omitted as it is not required in theillustration of how the cyclic `-ambiguity is resolved. v

At station B there is a transmitter 72 which :transmits a frequency (b).At station A there is a transmitter 61 that transmits a carrierfrequency (a) which differs from (b) by a low beat frequency (a-b).Receiver 62 at location A' receives frequencies (a) fand Cb), ampliiiesthem and extracts lthe beat frequency (a-b). Frequency divider 64divides this frequency by a factor K and modulates the transmitter 61through modulator 65 with the divided beat frequency. n At the positionto be determined S, an RF. amplifier 77 picks up the Vfrequencies (a)and (b) plus the modulation on frequency (a). =Filters 79 'and 80extract Vthe 'frequencies (a-b) and a divided "frequency The dividedfrequency is then fed to a multiplier 83 which multiplies by the samefactor K thus restoring the original frequency (a-b). These ktwofrequencies `are then compared in a phase meter 85 giving aphase angledifference 01,

v-At -station lA' there is another transmitter k66 which transmits afrequency `(d) which differs from frequency At station B', a transmitter67 transmits a frequency (e), and a receiver 68 `receives frequencies(d) and (e) and generates a low beat frequency (d-e) which is equal to(a-b). A frequency divider 70 connected to receiver 68 generates themodulation frequency (d-e) K -is also fed from the frequency divider70-to the phase detector 75. The frequency (aj-b) is'also supplied tothe phase detector 75 from'the receiver 73. These two dividedfrequencies are compared in f phase by the phase detector 75 whichprovides an error -voltage proportional tothe phase diiference to the`frequency controller 76 which changes thefrequency (b) lof transmitter72 proportionally to the error signal in order to reduce the phasediiferenceat phase detector 75 to zero. Therefore, this operationsynchronizes the modulation frequencies of thetwo different systems.

At the' position to be-determined, 'S, radio lfrequency amplifier 78receives frequencies (d) and (e) and the Amodulation frequency vTheamplifier 78 is connected to'two iilters 8'1 and 82 which-extract thefrequencies (d-a'e) and Y (dr-) respectively. The frequency an csimilarly, lthe phase difference 0.2 measured by phase meter 87 equals0= (M-l-Ra-RQ (19) a2=2-tM+Rb-na 20 Equation 19 shows that 61 isproportional to a constant term M plus the difference between distancesRa and Rb in terms of the vlI 'wave-length] wavelength of frequency (b).

Similarly Equation 20fshows -that 02 lis proportional to aconstant termM plus the difference between the dis- -tances YR., and Rb in terms ofthe wavelength of frequency=(d).

Accordingly, therefore, 01 or zrnay be read and this reading vwilldeline a hyperbola of constant phase difference betw'een Ra :and Rb,exactly as in standard loran procedure wherein avconstant timedifference is measured. This measurement lis in terms of the wavelengthof the carrier frequency used, and the accuracy of the measurement isapproximately one-hundredth of a wavelength ofthe carrier frequency, asthat amount kof phase difference may be conveniently measured.

However, in order to `avoid ycyclic ambiguity in the above finemeasurement, coarse and medium measurements at lower frequencies areprovided as will be shown in 'the .following discussion.

If H1 and 02 are added we have the following:

YEquation 2l shows that `@rl-02 is equal to a constant term plus thedifference `between Raand Rb in terms of the `wavelengths of the systemdifference frequency (b-d). Therefore, `the readingof 01+H2-in indicator88 will enable theresolution of cyclic ambiguity in the carrierfrequency 1 reading 61.

The phase angle 03'between'the two [modulation] low beat frequencieswhich is determined by phase meter 86 is likewise-dependent upon thedifference of the distances'to the two transmitting stations A and B.This can be shown as follows:

From Equation l5 we see that the [modulation] lo-w beatffrequency; ie.,the output of the multiplier 8.3; derived in the-navigation receiverat Sfrom the modulation component of the wave received from station A, is:

Likewise the [modulation] low beat frequency; Le.,

V'the 'output of the multiplier 84; derived' from the modulationcomponent of the 'carrier e received from station 'B [upon carrier e]is:

Remembering that the frequency control 7 '6 at station B makes the beatfrequencies synchronous, so that the phase angle between the[modulation] low beat frequencies from the multipliers 8.3 and 84 at thereceiver is 03, where Equation 24 shows that the phase angle 93 betweenthe modulation frequencies is likewise dependent upo-n the difference ofthe distances to the two stations, with the indication in terms ofwavelengths of the [modulation] low beat frequency (a-b). The reading ofthis phase angle 03, obtained from phase detector 86, provides a coarsereading at the longer modulation wavelength which resolves the cyclicambiguity in the higher frequency medium reading, (614-02).

In developing the equations for the phase angles, all of the delays,including fixed delays such as those due to the time of transit of thevarious waves between stations, were included. However, the zerorefe-rence for the phase angles may be shifted to the line where R,=`Rb,apd the Equations 19, 20 and 24 `for the phase angles 01, 02 and 63would become i- E) AAE gir-(C AR- Ab where 01 is proportional to AR interms of the wavelength of frequency b Where 02 is proportional to AR interms of the wavelength of frequency d ab AR= AR where 63 isproportional to AR in terms of the wavelength [rnodulation] low beatfrequency (a-b) where and 7( represents the wavelength of the subscriptfrequency. Also; from Equation 2l, dropping the constant term we have211 Arb-a) and a preferable ratio is 400:20:l.

The phase Shifters can be expected to measure to about 1% of a cycle,hence 03 will indicate AR to about which is less than ?\(b-d), a-nd014-02 will indicate AR to about .OlMb-d) which is less than )((b).

Therefore the system will resolve all ambiguities in up to fullwavelengths of the modulation frequency.

In a specific instance the carrier frequencies may be approximately 78kc. and 82 kc., the system difference frequency about 4 kc., and the[modulation] low bea't frequency about 200 cycles. A Wavelength at 200cycles is 932 miles. Since the maximum phase shift is twice thebaseline, in wavelengths, a system with a 450 mile baseline betweenstations would have no ambiguities with a carrier frequencyapproximately of kc.

Fig. 8 is a block diagram of a three station system, which is therequired number of stations to provide a navigational fix. This systemis similar to that yof Fig. 7 with the addition of a third station C,which is essentially similar to station B. Station B is identical withstation B of Fig. 7 and cooperates with station A, as described inconnection with Fig. 7, to define the hyperbola O of constant phasedifference in the range AB.

Station C cooperates with station A in a similar manner to dene ahyperbole. P in the range AC. This is done with the same technique asdescribed in detail in connection with Fig. 7. However, differentfrequencies must be used in order to differentiate the signals at thereceiving location.

Station C generates a frequency (c) in transmitter 72 and a frequencyy'(f) in transmitter 67. Receiver 68 receives frequencies (d) a-nd (f)and receiver 73 receives frequencies (a) and (c). Frequencies (la-c) and(d-f) are compared in phase detector '75' and synchronized through theoperation of frequency controller 76' which controls the frequency (c)of transmitter 72'. The difference frequency (d-f) is also modulated oncarrier (f) of transmitter 67. All of the iabove mentioned units ofstation C are the same `as those of station B with the exception thatdifferent frequencies are used.

Station A is the same as in lFig. 7 except that a second filter divider64 has been added to the output of receiver [61] 62 to extract thefrequency.

(a-G) K from the output of receiver [61] 62 in addition to the signalextracted by the filter divider 64 at frequency.

(2l-b) K azbSa-I) and eig-gi)- The output of this R.F. amplifier isapplied to four filters 91, 92, 93 and 94 which extract respectivelyfrequencies (af-JD): K

y (ade) and (2L-C) K ei-Me) (e-f) K K and fj;

The output of RJ?. amplier 102 is connected to four 1l filters; 103.,104,` 105 and 1,06,

which extract respectively frequencies (d e), (fm) and LK@ The, twodivided frequencies are multiplied by a factor of K in the multipliers107 and 108 to restore the original frequencies. The separately derived(d-e) frequencies are compared in phase meter 109, providing lameasurement of 92 for the AB range; and separately derived (fd)frequencies are compared in phase meter 110, providing a measurement of02 in the AC range.

The [modulation] low beat frequencies (a`b) and (d-e) from multipliers95 and 108 are applied' to phase meter 111 Where they are compared togive the coarse measurement 03 of the phase difference in the AB range.As previously explained, this coarse position is based upon the long andtherefore unambiguous wavelength of the [modulation] low beat frequency(a-b).

The (a-c) [modulation] low beat frequency and the ('f-d) [modulation]low beat frequency are similarly compared in the phase meter 112 toprovide a measure ment of 03 in the AC range.

The readings in the AB range are combined in indicator 113 to therebyprovide a coarse, a medium and a line reading which will identifyhyperbola O.

The 0 readings in the AC range are combined in indicator 114 to therebyprovide a coarse, a medium and a fine reading which will definehyperbola P.

In the AB range indicator 113 the coarse reading is provided byindicator 1,40 which merely repeats the reading 93 of phase detector111. The medium reading is provided 'by indicator 141 which adds the 01reading from phase detector 100, and the 02 reading from phase detector109. This addition may be done mechanically as by a differential. Theline reading is provided by indicator 142 which repeats the 02 readingof phase detector 109.

In the AC range indicator 114 the coarse provided by indicator 143 whichrepeats the 03 reading of phase meter 1112. The medium reading isprovided by indicator 144 which adds 01 reading from phase detector 101and the 02 reading from phase detector 110. The line reading is providedby indicator 145 which repeats H2 reading which is derived by phasedetector 110.

The readings from indicators 113 and 114 may be referred to a previouslyprepared chart such as` used with standard loran, in order to determinethe navigational fix.

One method of combining the three dial readings in indicators 113 and114 to get a composite reading, may be illustrated in a typical exampleas follows:

Assume we have two transmitting stations M and N separated by l/m of the(modulation) frequency. Then as a receiver is moved from M to N,remembering the frequency ratio of carrierzsystem diiferencmmodulationis 400:20: l, the values are chosen so that:

reading is The coarse dial (03) will turn l revolution,

The medium dial (014-02) will turn 20 revolutions,

and

The tine dial (01) will turn 400 revolutions.

It must be noted that as a receiver is moved V2A from one station, italso moves V2A closer to the other station, so that the total phasedifference is Ik.

The, dials may be conveniently calibrated in arbitrary distance units,the total distance being 400 units such that:

lrevolution of the line dial=1k unit l revolution of the medium dial=20units l revolution of the coarse dia1=400 units Suppose the receiver isput at the location to be determined, which is in fact, .632 of thetotal distance, or

12 252.8 distance units along the line joining the. twoy stations. Thephase angle difference 01 will be cycles, i.c., if the receiver had beenmovedy from the point of zero distance, the fine dial would have turned252.8 revolutions. The number of complete cycles are not indicated onthe dial, and therefore, the fine dial reading is .8 revolution which isequal to .8 units.

Similarly, if the receiver had been moved from zero the medium dialwould have turned 20X.63,2=12.64 revolutions. As the full cycles are notindicated, the only significant portion is .64 revolutions which, as thedial has 20 distance -units per revolution is equal to 12+ units.

Similarly, if the receiver had been moved lfrom zero position, thecoarse dial would have turned .632 revolutions. As this dial iscalibrated with 400 distance units the reading to its allowabletolerance will be 240+ units.

The operator may add the readings to obtain the posi tion in distanceunits equal to 252.8 units.

Alternatively, an additive mechanism might easily be provided to furnishthe final reading without any computation on the operators part.

The dial markings must be chosen to be read with an accuracy,proportional to the allowable tolerance in that particular part of thesystem. The lower frequency dials resolve cyclic .ambiguity of phaseshift of the highest frequency, without regard to the previous historyof motion of the receiver. The receiver does not have to be set at aknown location and kept in continuous operation, which would be the caseif the medium and coarse dials were merely cycle counters of the finedial. The equipment may be turned on, at the unknown location withoutany pre-setting and will immediately give the correct reading.

Fig. 9 illustrates apparatus to indicate phase difference which may beused in the phase meters such as 85, 86 and 87 of Fig. 7. The referencephase voltage is connected to the input transformer 150, the secondaryof which is connected to a phase-splitting network for the purpose ofdividing the single phase input into a three phase volt-age to energizethe stator windings 151, 152 and \153 of self-synchronous transformer orSelsyn 160. The phase-splitting circuit, comprising adjustable condenser155 and adjustable resistor 156, is connected across stator arms 151 and152. The values of condenseris 155 and 156 are chosen so as to provide abalanced three phase voltage across the three stator arms when a singlephase voltage is applied to the input.

The rotor 157 of the Selsyn 160 is adapted to be turned by motor 158 andshaft 169 t-o thereby produce a phase shifted Selsyn output voltageacross the rotor 157 winding. The beat frequency phase voltage to beCOmPICd with the reference phase voltage is applied to the primary oftransformer 16-1, and each end of the secondary of the transformer 161is connected to the plates of a pair of diodes 162 and 163. The cathodesof the diodes are connected to a balanced resistor-capacitance network165. The reference phase voltage (ER) output from the rotor 157 isconnected between the center tap of the secondary of transformer 161 andthe center of the balanced out,- put network 165.

When the two signals are in phase, the zero position of rotor 157 ischosen so that ER is 90 out of phase with EA and EB as `shown in Fig.10. The resulting voltage vectorsy Ec and ED, are -equal in amplitudeand their rectiiied outputs balance each other in the network providingzero output.

lf there is a phase shift in one direction as illustrated in Fig. l1,lthe amplitude o-f ED becomes larger vand the amplitude of EC becomessmaller. If the phase yshift had been in the opposite direction EC wouldhave become assai larger and ED smaller. These two voltages EC and Enare rectified in the diodes 16-2 and 163 and these rectified voltagesare opposed in network 165, thereby providing a D C. error voltage Whoseamplitude and polarity is proportional to the magnitude and sense of thephase difference.

This error voltage generated across the output network 165 is applied tothe `input of amplifier 166 which energizes motor 158 so as to turnrotor 157 in a direction which will reduce the phase difference to zero.When this is done the desired phase reading 01, 02, or 63 may be readfrom dial 170.

Thus it is seen that cyclic ambiguity is resolved by utilizing twochannels slightly separated in frequency. The difference frequencybetween the channels may be effectively utilized as a second systemwhose wavelength is long enough so that its phase shift is substantiallyunambiguous. This lo-nger wavelength system is used as a medium readingto resolve ambiguity in the fine high frequency readings. A furtherextension of the non-ambiguous range is obtained by using synchronizedlow frequency modulation signals on the above-mentioned pair of carrierchannels. These modulation frequencies are utilized as a third coarsesystem having a [wave length] wavelength long enough to resolveambiguities in the medium system.

These various frequencies must be suitably chosen to obtain the bestcoverage. A ratio of approximately 20 to l between the carrier frequencyand the difference frequency between the carrier channels, and `asimilar ratio of `approximately 20 to l between the system differencefrequency and the law baat signal used to develop the modulationfrequency has been 'found preferable in one embodiment of the invention.The actual choice of frequencies must -be governed by designconsiderations such as, coverage desired, length of available baseline,frequencies available and propagation and other factors.

Since many changes could be made in the above construction iand manyapparent-ly widely different embodiments of this invention could be madewithout departure from the scope thereof, it is intended that all mattercontained in the above-description or shown in the accompanying drawingsshall be interpreted as illustrative `and not in a limiting sense.

What is claimed is:

[l. In a radio navigation system of the type wherein continuous wavesignals are transmitted from three separate locations, and first andsecond beat frequency waves derived from said three signals aretransmitted separately from -said transmitting locations; a receiver,comprising first receiving means adapted to receive said first threesignals, second receiving means adapted to receive said first and secondbeat frequencies, detecting means. responsive to said first receivingmeans to obtain said first and second beat frequencies directly fromsaid first three signals, filter means responsive to said secondreceiving means to separate said first and second beat frequencies,first phase comparison means responsive to said filter means and saiddetecting means to compare in phase said separately received first beatfrequencies, second phase comparison means responsive to said filtermeans and said detecting means to compare in phase said separatelyreceived second beat frequencies] [2. In a radio navigation system ofthe type wherein continuous wave signals are transmitted from threeseparate locations, and first and second beat frequency waves derivedfrom `said three signals are transmitted as a modulation from saidtransmitting locations; a receiver comprising means to receive saidthree continuous wave signails, means responsive to said receiving meansto obtain said first `and second beat frequencies by mixing said threecontinuous wave signals, filter means responsive to said receiving meansto obtain said first and second beat frequency modulations, and firstphase comparison means to compare in phase said first lbeat frequencyand said first 14 beat frequency modul-ation signals, and second phaseconiparison means to compare in phase said second beat frequency andsaid second beat frequency modulation signals] [3. ln a radio navigationsystem of the type wherein continuous wave signals are transmitted fromthree separated locations, and first and second beat frequency wavesderived from .said three signals `are transm-itted as a modulation fromsaid transmitting locations; a receiver comprising means to receive saidthree continuous wave signais including said modulations, detectingmeans responsive to said receiving means, first filter means responsiveto said detecting means to obtain said first beat frequency, secondfilter means responsive to said detector means to obtain said first beatfrequency modulation, phase comparison means responsive to said firstand second filter means to compare the phase thereof, third filter meansresponsive to said detecting means to obtain said `second beatfrequency, fourth filter means responsive to said detector means toobtain said second ybeat frequency modulation and phase comparison meansresponsive to said third and fourth lter means to compare the phasethereof; to thereby determine the position of said receiving locationwith reference to predetermined hyperbolic lines of position relative tosaid three transmitting locations] 4. Means to `obtain navigationalposition by radio means without cyclic ambiguity comprising means totransmit a first continuous wave signal from a first location, means totransmit a second continuous wave signal from a second location, meansto receive said first and second signal at said first location and meansconnected to said receiving means to mix said first and second signalsto thereby obtain abeat frequency, means to divide said beat frequency,means to modulate said first signal with said divided beat frequency,means t-o transmit a third continuous wave signal from said firstlocation, means to transmit a fourth continuous wave signal from saidsecond location, means to receive `said third and fourth continuous wavesignals at said second location, means to mix said third and fourthreceived signal and to divide the resultant beat frequency, means tomodulate said fourth continuous Wave signal with said divided beatfrequency, receiving means at said second loc-ation iadapted to receivesaid first and second signals, means to mix said first and secondsignals to obtain a beat frequency including means to divide said beatfrequency, phase comparison means connected to said third receivingmeans and to said modulating means and adopted to measure the phasedifference between the divided beat frequency of said first and secondsignals :and the divided beat frequency of said third and fourthsignals, -frequency control means responsive to said phase detectingmeans adapted to vary the frequency of said second signal transmitting-means to reduce said phase difference to zero, receiving means at `athird location adapted to receive said first and second signals, filtermeans connected to said receiving means adapted to obtain the lbeatfrequency between said first and second signals, second filter meansconnected to said receiving means adapted to obtain said divided beatfrequency of said first and second signals first multiplication meansconnected to said divided filter adopted to multiply said dividedfrequency to its original value, first phase detecting means connectedto said multiplication means and said first filter means, secondreceiving means at said third location `adapted to receive said thirdyand Ifourth signals, third filter means connected to said secondreceiving means `adapted to obtain the beat frequency of said third yandfourth signals, fourth filter means connected to said receiving meansand adapted to obtain the -divided beat frequency, of said third and`fourth signals, second multiplication means connected to said dividedAfrequency filter means, to restore said divided beat frequency to itsoriginal value, second phase detecting means connected to said thirdfilter means and said second multiplication means to measure the phasedifference therebetween, and third phase detecting means connected tosaid first and second multiplication means to measure the phasedifference therebetween.

5. Means for yobtaining a locus of navigational position by radio meansWithout cyclic ambiguity, comprising means for obtaining a beatfrequency at the receiving location from a pair of signals received`from separate transmitting locations, means for obtaining said beatfrequency at the, first of said transmitting locations and separatelytransmitting it to said receiving location as a modulation, means forobtaining a second beat frequency at said receiving location `from asecond pair of signals received from said separate transmittinglocations, means for obtaining said second beat frequency at the secondof said transmitting locations and transmitting it to said receivinglocation as a modulation, means for compairing the phase of saidseparately received first beat frequencies at said receiving location,means for comparing the phase of said separately received second beatfrequencies at said receiving location and means for comparing the phaseof said separately received modulation frequencies at said receivinglocation to thereby determine the hyperbolic locus of positions of saidreceiving location relative to said transmitting locations with accuracyproportional to the highest frequency and without cyclic ambiguity.

6. Means for resolving cyclic ambiguity in continuous wave navigationsystems, comprising means for obtaining a beat frequency at a receivinglocation from a pair of signals received from separate transmittinglocations, means for deriving said beat frequency separately at thefirst of said transmitting locations and transmitting it to saidreceiving location as a modulation, means for obtaining a second beatfrequency at said receiving location from a second pair of signalsreceived from said separate transmitting locations, means for derivingsaid second beat frequency at the second of said transmitting locationsand transmitting it to said receiving location, means for obtaining saidfirst beat frequency at said second location, means for comparing thephase at said second location of said first and second beat frequenciesand means for controlling the frequency of the signal of said first pairof signals transmitted from said second location to reduce the phasedifference to zero, and means at said receiving location means forcomparing the phase of said first beat frequencies, means for comparingthe phase of said second beat frequencies and means for comparing thephase of said modulation beat frequencies.

7. Means for obtaining a navigational fix by radio means without cyclicambiguity, comprising means for obtaining a beat frequency :at areceiving location from a pair of signals received from separatetransmitting locations, means for deriving said beat frequencyseparately at the iirst of said transmitting locations and transmittingit lto said receiving location as a modulation, means for obtaining asecond beat frequency at said receiving location from a second pair ofsignals received from said separate transmitting locations, means forderiving said second beat frequency at the second of said transmittinglocations and transmitting it to said receiving location, means forobtaining said first beat frequency at said second location, means forcomparing the phase at said ysecond location of said first and secondbeat frequencies and controlling the frequency of the signal of saidfirst pair of signals transmitted from said second location to reducethe phase difference to zero, means for comparing the phase of saidfirst beat frequencies, means for comparing the phase of said secondbeat frequencies and means for comparing the phase of said modulationbeat frequencies at said receiving location.

8. A coarse and [fine hyperbolic navigation system comprising, means atat least two separate :locations vto transmit at least two continuous.wave signals each,

vmeans ,at at kleast one of said locations to receive said signals,means responsive to said receiving means to generatesubharmonicmodulation products from Said f l5 signals, and means to retransmit saidmodulation prod@ ucts to thereby establish coarse and -fine hyperboliclines of position relative to said locations.

9. Craft receiving means comprising means to receive signals from twoseparate locations, means responsive to said first means to detectmodulation products from said signals, means to receive separatesubhanmonic modulation products from at least one of said :loca-tions,means to compare said modulation products `to thereby determine thecraft position relative to said locations, and means to resolveambiguities of said comparison.

10. Navigation apparatus comprising means to receive a plurality ofseparate frequency signals and a plurality of separate modulations,means to generate a plurality of modulation products from said signals,means to compare in phase said modulations with said generatedmodulation products, means to indicate said phase difference in terms oftwo of said signal wavelengths, and means to resolve cyclic ambiguity ofeach, of said phase differences including means to combine said phasedifferences.

1l. A coarse and fine navigation system comprising, first and secondcontinuous wave hyperbolic navigation systems of the type transmittingnonsynchronous continuous wave signals `from separate transmitters andtransmitting a beat frequency reference modulation from one of thetransmitters, first and second receiving means responsive to thefrequencies of said first and second transmitting systems to measuredistance, means to resolve cyclic ambiguity of measurement of said firstand second systems comprising third receiving means responsive to thedifference frequency between said first and second transmitting systems.

12. A coarse and fine navigation system comprising, first and secondcontinuous wave hyperbolic navigation systems of the type transmittingnonsynchronous continuous wave signals from separate transmitters, andtransmitting a beat frequency reference modulation from one of thetransmitters, first and second receiving means responsive to thefrequencies of said first and second transmitting systems and havingiii-st and second phasemeters to measure distance, means to resolvecyclic ambiguity of measurement of -said first and second systemscomprising means for adding the outputs of said .iirst and secondphasemeters to provide la distance measurement in terms of thedifference frequency between said first and second transmitting systems.

13. A coarse, medium and fine navigation system comprising, first andsecond continuous wave hyperbolic navigation systems of the typetransmitting nonsynchronous modulated continuous wave signals fromseparate .transmitters and transmitting a beat frequency referencemodulation from one of the transmitters, first and second receivingmeans responsive to the frequencies of said first and secondtransmitting systems, means to resolve cyclic ambiguity of measurementof said first and s econd systems comprising third receiving meansresponsive to the difference frequency between said first and secondtransmitting systems, and means -to resolve cyclim ambiguity of saidsystem difference frequency distance measurement comprising fourthreceiving means responsive to said modulation frequency. Y

14. A coarse, medium and fine navigation system comprising, first andsecond continuous wave hyperbolic navigation systems of the typetransmitting nonsynchronous modulated continuous wave signals fromseparate transmitters and transmitting a beat frequency referencemodulation fro-m one of the transmitters, first and second receivingmeans responsive to the frequencies of said first and secondtransmitting systems, means to resolve cyclic ambiguity of measurementof said first and second systems comprising third receiving meansresponsive to the difference `frequency between said `first and secondtransmitting systems, and means to resolve krcyclic ambiguity of saidsystem difference frequency 17 measurement comprising a -phasemeiet'responsive to said modulation frequency.

15. In a position indicating system, means for translating spaceradiated signals into p-osition indications comprising, means forobtaining a first beat frequency signal at a receiving location from afirst pair of signals received from separate transmitting locations,means for obtaining a second beat frequency signal at said receivinglocation from a second pair of signals received from said separatetransmitting locations, means at one of said transmitting locations forobtaining said first and second beat frequency signals, mea-ns at saidone transmitting location jointly responsive to said first and secondbeat frequency signals for controlling the frequency of at least one ofsaid space radiated signals to maintain the phase difference betweensaid beat frequency signals at a predetermined value and thus maintainthe same beat frequency value between said first and second pairs ofsignals, and means at said receiving location jointly responsive to saidfirst and second beat frequency signals to produce a positionindication.

16. A wave signal transmission system comprising, a pair of spacedtransmitting units, a plurality of pairs of transmitters for radiatingsignals of different frequencies, said transmitters of each pair beingrespectively disposed at dierent transmitting units, means at one ofsaid transmitting units for obtaining a first beat frequency signal fromthe signals radiated by a first pair of said transmitters, means at saidone unit for obtaining a second beat frequency signal from the signalsradiated by a second pair of said transmitters, and means at said oneunit responsive to at least one of said beat frequency signals forcontrolling the frequency of at least one of said transmitters tomaintain the same beat frequency between said first and second pairs ofsignals.

17. A wave signal transmission system comprising, a pair of spacedtransmitting units, a plurality of pairs of transmitters for radiatingsignals of different frequencies, said transmitters of each pair beingrespectively disposed at different transmitting units, means at one ofsaid tran-smitting units for obtaining a first beat frequency signalfrom the signals radiated by a first pair of said transmitters, means atsaid one unit for obtaining a second beat frequency signal from thesignals radiated by a second pair of said transmitters, and means atsaid one unit responsive to at least two of said signals for controllingtlie frequency of at least one of said transmitters to maintain apredetermined phase difference between said beat frequency signals.

18. A wave signal transmission system comprising, a pair of spacedtransmitting units, a plurality of pairs of transmitters for radiatingsignals of different frequencies, said transmitters of each pair beingrespectively disposed at different transmitting units, means at one ofsaid transmitting units for obtaining a first beat frequency signal fromthe signals radiated by a first pair of said transmitters, means at saidone unit for obtaining a second beat frequency signal from the signalsradiated by a second pair of said transmitters, means at said one unitfor comparing the phase of said beat frequency signals, and meanscontrolled by said phase comparing means for controlling the frequencyof at least one of said transmitters to maintain at a predeterminedvalue the phase difference between said beat frequency signals.

19. Means for resolving cyclic ambiguity in continuous wave navigationsystems, comprising means for obtaining a beat frequency signal at areceiving location from a pair of signals received from separatetransmitting locations, means for obtaining a second beat frequencysignal at said receiving location from a second pair of signals receivedfrom said separate transmitting locations, means for obtaining saidJirst and second b'eat frequency signals at one of said transmittinglocations, means at said one transmitting location jointly responsive tosaid first and second beat frequency signals for controlling the fre- 18quency of at least one of said transmitted signals to maintain at apredetermined value the phase difference between said beat frequencysignals, and means at said receiving location for obtaining a positionindication in response to said first and second beat frequlency signals.

20. In a position indicating system, means for translating spaceradiated signals into position indications comprising, means forobtaining a first beat frequency signal at a receiving location from afirst pair of signals received from separate transmitting locations,means for obtaining a second beat frequency signal at said receivinglocation from a second pair of signals received from separatetransmitting locations, means at one of said transmitting locations forobtaining said first and second beat frequency signals, means at saidone transmitting location for transmitting a reference signal derivedfrom at least one of said beat frequency signals to said receivinglocation as a modulation, means at said one transmitting locationjointly responsive to said first and second beat frequency signals forcontrolling the frequency of one of said transmitted signals to maintainat a predetermined value the phase dierence between said beat frequencysignals, means at said receiving location for comparing the phase ofsaid modulation with the corresponding beat frequency signal to produceone position indication, and means at said receiving location jointlyresponsive to said first and second beat frequency signals for producinganother position indication.

21. A wave signal transmission system comprising, a pair of spacedtransmitting units, a plurality of pairs of transmitters for radiatingsignals of dierent frequencies, said transmitters of each pair beingrespectively disposed at different transmitting units, means at one ofsaid transmitting units for obtaining a first beat frequency signal fromthe signals radiated by a first pair fo said transmitters, means at saidone unit for obtaining a second beat frequency signal from the signalsradiated by a second pair of said transmitters, means at said one unitfor modulating a reference signal derived from at least one of said beatfrequency signals on thle signal radiated by one of said transmitters atsaid one unit, means at said one unit controlled by the phaserelationship between said beat frequency signals for controlling thefrequency of the signal radiated by one of said transmitters to maintainthe beat frequency between the signals radiated by said Jirst pair oftransmitters equal to the beat fnequency between the signals radiated bysaid second pair of transmitters.

22. In a position .indicating system, means for translating spaceradiated signals into position indications comprising receiving meansfor receiving a plurality of pairs of space radiated signals and forheterodyning said received pairs to produce beat frequency signalshaving frequencies respectively related to the beat frequencies betweenthe signals of each pair, means for receiving at least one modulatedspace radiated carrier signal and for developing therefrom referencesignals having frequencies respectively equal to said beat frequencysignals, means for phase comparing an lequal frequency pair of said beatfrequency signals and reference signals to provide at least one positionindication, means for mixing said beat frequency signals and saidreference signals, and means responsive to the output of said mixingmeans for producing at least o-ne other position indication.

23. Wave signal receiving apparatus for translating received spaceradiated signals into position indications comprising, a plurality ofreceivers for respectively receiving pairs of spalce radiated signalsand for heterodyning said received pairs to produce beat frequencysignals having frequencies respectively representative of the beatfrequencies between the signals of each pair, means for receiving amodulated space radiated carrier signal and for developing from thiemodulation components thereof reference signals having frequenciesrespectively equal to said beat frequency signals, first phasecomparison I9 means energized by one of said beatA frequency signals andthe corresponding one ofsaid reference signals, second phasecomparisonmeans energized by the otherk beat frequency signal and referencesignal, and.` dierential means responsive to the outputs of said phasecomparison means for providing position indications.`

24. A fine and coarse position determining system, comprising jrsttandsecond continuouswave systems of the type transmittingnon-synchronizedxwave signals from separate transmitters and prov-idingbeat frequency signals used in developing reference signals fortransmission, receiving means responsiv'e to the wave signalsand*reference signals of one of said systems to provide a positionindication related to the frequency of-` the'wave signals of said onesystem., and means to resolve the cyclic ambiguity ofsaid positionindications comprising means to provide a positionindication in terms ofthe difference frequency between said first andsecond systems.

25; A system for providing fine and coarse position indications,comprising rstand second continuous wave transmission systems eachincluding spaced non-synchronized transmitters for transmittingcontinuous wave signals from separate points totA produce beat frequencysignals and including means for radiating reference signals derived fromsaid beat frequency signals, receiving means responsive to thle wavesignals and reference signals of one of said systems to provide oneofsaid position indications related to the frequencyxof the wave signalsof said one system, and means responsive to the wave signals andreference signals. of both 'of said systems to provide the other of saidvposition indications related to the relative. values -of thefrequencies of said rst and second systems.

26. A system for providing `position indications, comprising first andsecond continuous wave transmission systems eachincludingrspacednon-synchronized transmitters for transmitting,continuous wave signals from separate `points to produce beat` frequencysignals and including means forv radiatingreference signals derived fromsaidv beat frequency signals, and receiving means responsive to the`wave signals and reference signals of both of said systems for providingposition indications related to the relative valuesof thefvfrequenciesof said rst and second systems.

27. A system for providing position indications, comprising )rst andsecond continuous wave transmission systems eac'h. including spacednon-synchronized transmitters for transmitting continuous wave signalsin pairs from at least two separated points, the signal frequenciesutilized in said first system being different from the signalfrequencies utilized in said second system; and receiving meansresponsiveto the wave signals of both of saidI systems for.y providingposition indications related to the relative values of the signalfrequencies utilized in said first and second systems.

28. A fine' and coarse position determining system, comprising first andsecond continuous wave systems of the type transmitting non-synchronizedwave signals from separate transmitters andpro-viding beat frequencysignals for use in devel'opingfreferencer signals for transmission,receiving means responsive to the wave signals and reference signals ofone of said systems for providing a position indication related to thefrequency' of the-wave signals of said one system, and means to resolvethe cyclic ambiguity of said position indications including meansresponsive to thewave signals of both of said systems for providing asecond position indication related to the frequency difference betweenthe wave signals of said first and second systems.

29. In a position determining system, a pair of continuous wave systemsof the type transmitting non-synchronized wave signals from separatetransmitters and providing beat frequency signals forr use in developingreference signals for transmission, `said rsystems operating at.dierentfrequencies,` receiver means-for each ofV said systems for receivingsaid different frequency signals, and means responsive to the outputs ofsaid receiver means for providing a position indication related to thefrequency dierence betweenl the wave signals of said pair of systems.

30. Wave signal receiving apparatus comprising means to receive aplurality of pairs of signals radiated from two separate locations, saidpairs of signals being of distinguishably different frequencies, and thetwo signals forming each pair being radiated from different locationsand each pair of signals haivng the same frequency separation, saidreceiving apparatus including means for heterodyning the signals of arst of said pairs to pr duce a first beat frequency and for heterodyningthe signals of a second of said pairs to produce a second beat frequencysignal equal in frequency to the first beat frequency signal, and meansjointly responsive to said beat frequency signals to provide a positionindication related tothe frequency difference between said pairs.

31. In a system for determining the location of a receiving pointrespective to spaced transmitters by comparing at said receiving poin-tthe phases of signals emitted by said transmitters and received at saidreceiving point, at least two spacedv transmitters for emittingcontinuously at least three dierent non-synchronized high frequencywaves, `the choice of saidL frequencies being limited by the onlycon-dition which is suyficient and necessary that the algebraic sumofthe respective products of said frequencies by any integers, at leastone of which is positive and at least one of which is negative, is zero,at said receiving point: a receiver comprising in combination filtering,amplifying and mixing means to receive said waves and deduce therefromby `means of differing frequency mixtures two currents having the samefrequency and phasemetering means jointly responsive to said twocurrents for providing an indication concerning the location of saidreceiving point respective to said transmitters.

32. In a systemy for determining the location of a receiving pointrespective to spaced transmitters by comparing at said receiving pointthe phases of signals emitted by said transmitters and received at saidreceiving point, at least two spaced transmitters for emitting at leastthree different high frequency waves, the choice of said frequenciesbeing limited by the only condition which are suicient and necessarythat the algebraic sum of the-respective products of said frequencies byany integers, at least one of which is positive and at least one ofwhich is negative, is at least substantially zero, means for cancellingsaid algebraic sum and for automatically maintaining it at zero, saidmeans comprising in combination: a receiver comprising in combinationltering, amplifying and mixing means, to receive said waves and todeduce therefrom by means of frequency mixtures two currents thedifference between the frequencies of which is equal to said algebraicsum and means responsive to the difference between the frequencies andthe difference between the phases of said two currents to act upon thefrequency and the phase of one of said emitted waves to cancel saidfrequency difference and consequently to cancel said algebraic sum, atsaid receiving point: a receiver comprising in combination filtering,amplifying and mixing means to receive said waves and deduce therefromby means of differing frequency mixtures two currents having the samefrequency and phasemetering means jointly responsive to said twocurrents for providing an indication concerning the location of saidreceiving point respective to said transmitters.

33. In a system for determining the location of a receiving pointrespective to spaced transmitters by comparing at said receiving pointthe phases of signals' emitted by said transmitters and received at saidreceiving point, at least two spaced transmitters to emit continuouslyfour dierent continuous, non-synchronized high frequencywaves subject tothe only condition that the difference between vtwo of said frequenciesis equal to the difference between two other frequencies, a receivercomprising in combination ltering, amplifying and mixing means toreceive said waves and deduce therefrom by means of differing frequencymixtures two currents having the same frequency and phasemetering meansjointly responsive to said two currents for providing an indicationconcerning the location of said receiving point respective to saidtransmitters.

34. In a system for determining the location of a receiving pointrespective to spaced transmitters by comparing at said receiving pointthe phases of signals emitted by said transmitters and received at saidre'ceiving point, at least two spaced transmitters to emit fourdifferent continuous high frequency waves, the choice of thesefrequencies being limited by the only condition that the differencebetween two of said frequencies is at least substantially equal to thedifference between two other frequencies, means for rendering equal saidtwo differences and for automatically maintaining them equal, said meanscomprising in combination: a receiver comprising in combinationfiltering, amplifying and mixing means to receive said waves and deducetherefrom by differing frequency mixtures two currents the dierencebetween the frequencies of which is equal to the difference of saidabove mentioned frequency differences, and means responsive to thedifference between the frequencies and the difference between the phasesof said two currents to control one of said transmitters to regulate thefrequency and the phase of the wave emitted thereby to cancel said lastmentioned frequency difference and consequently to render equal said twofirst mentioned frequency differences, a receiver `at said receivingpoint comprising in combination filtering, amplifying and mixing meansto receive said waves and derive therefrom by means of differingfrequency mixtures two currents having the same frequency andphasemetering means jointly responsive to said two currents forproviding an indication Iconcerning the location of said receiving pointrespective to said transmitters.

35. In a system for determining the location of a receiving pointrespective to spaced transmitters by comparing at said receiving pointthe phases of signals emitted by said transmitters and received at saidreceiving point, at least two spaced transmitters to emit fourcontinuous high frequency waves, respectively having a first, a second,a third and a fourth frequency which are all different and the choice ofwhich is limited by the onlycondition that the beat between said firstand third frequencies on the one hand and between said second and fourthfrequencies on the other are equal low frequencies at said receivingpoint, the first and second frequency waves being radiated from one ofsaid transmitters and the third and fourth frequency waves beingradiated from the other transmitter, a receiver comprising in combination filtering, amplifying and mixing means to receive through a firstchannel said first and third frequencies and to detect the beat thereofand to receive through a second channel said second and fourthfrequencies and to detect the beat thereof, and phase metering meansjointly responsive to said two beats for providing an im dieationconcerning the position of said receiving point respective to saidtransmitters.

36. In a system for determining the location of a receiving pointrespective to spaced transmitters by coimparing at said receiving pointthe phases of signals emitted by said transmitters and received at saidreceiving point, two spaced transmitters to emit a first, a second, athird and a fourth continuous high frequency wave having respectively afirst, a second, a third and a fourth frequency, one of saidtransmitters emitting said first and second waves and the other saidthird and fourth waves, said frequencies being all different and theirchoice being subject to the only condition that the difference betweensaid first and third frequencies is equal to the difference of saidsecond and fourth frequencies, at said receiving point: a receivercomprising in combination filtering, amplifying and mixing means toreceive said waves and deduce therefrom by means of differing frequencymixtures two currents having the same frequency one of said currentsbeing derived by beating said first and third frequency waves and theother current being derived by beating said second and fourth frequencywaves, and phasemetering means jointly responsive to said two currentsfor providing an indication concerning the loca.- tion of said receivingpoint respective to said transmitters.

37. In a system` for determining the location of a receiving pointrelative to spaced transmitters, at least two spaced transmittersemitting continuously at least three different non-synchronized signalshaving frequencies which are independent of each other except that theysatisfy the relation where F1, F2 Fn are said frequencies and K1, K2, Knare integers at least one of which is positive and at least one of whichis negative, whereby two currents of the same frequency can be derivefdfrom said signals by combination filtering, mixing an'd amplifyingmeans, a receiver at said receiving point incluuding combinationamplifying, filtering and mixing means to receive said signals andderive therefrom two currents of the same frequency, and means jointlyresponsive' to the last-mentioned two currents for providing anindication about the position of said receiving point relative to saidtransmitters.

38. In a system-for determining the location of a receiving pointrelative to spaced transmitters by comparing at said receiving point thephases of signals emitted by said transmitters and received at saidreceiving point, at least two spaced transmitters for emitting at leastthree different high frequency signals having frequencies which satisfythe relation where F1, F2 F,L are said frequencies and K1, K3, L K7, areintegers at least one of which is positive and at least one of which isnegative, whereby two currents of equal frequency can be )derived fromsaid signals` by combination filtering, amplifying and mixing means, areceiver of fixed location having filtering, dmplifying and mixing meansto rece-ive said signals and derive therefrom two currents having thesame frequency when said relation is satisjed, one of said transmittershaving a frequency and phase regulating device, means responsive to thedifference between the frequencies and the difference between the phasesof said two currents derived by said receiver when said relation is notsatisfied to actuate said frequency and phase regulating device to causethe frequencies of said signals to again satisfy said relation, areceiver at said receiving point having filtering, amplifying and mixingmeans to receive said signals and derive therefrom two currents havingthe same frequency, and phase metering means jointly responsive to thelast-mentioned two currents for providing an indication concerning thelocation of said receiving point relative to said transmitters.

39. In a system for determining the position of a receiving point, atleast two spaced transmitters emitting signals of at least threefrequencies, means to regulate one of said frequencies so that saidfrequencies at least substantially satisfy the relation KlFl-l-KZFZ-i-KF=0 where F1, F2 Fn are the frequencies and K1, K2 Kn are integersat least one of which is positive and at least one of which is negative,whereby two currents can be derived from said signals by combinationfiltering, amplifying and mixing means which currents have the samefrequency when said relation is satisfied and have a frequency dyferencewhen said relation is not satisfied, said means including a frequencyvarying device in one of `said transmitters, means responsive to `all ofsaid signals and having combination amplifying, filtering and mixingmeans for deriving two currents from said signals and means responsiveto any )differences in frequency and phase between the last-mentionedtwo currents when said relation is not satisfied for actuating saidfrequency varying device to vary said one frequency to compensate forany lack of stability of the other frequencies "and cause said relationto be a'gain satisfied, a receiver at said receiving point havingcombined amplifying, filtering and mixing means `for Aderiving two`currents of the same frequency from said signals when said relation issatised, and means jointly .responsive toy the `last-mentioned twocurrents to provide an indication with respect to the position of saidreceiving point.

40. A fine .and coarse position determining system, comprisingtransmitting apparatus for emitting first and second pairs of `wavesignals from separate transmitters and also including meansforbeatingthe waves of at least one ofthe pairs together to'develop-beat signals used in deriving reference signals fortransmission, `the signals of the rfirst pair being distinguishable fromthe signals of the second pair, receiving means responsive to the wavesignals and reference signals `to provide ya first position indication,and means to resolve the cyclic ambiguity of said rst position:indication comprising lmeans to provide a second position indication interms `of the difference frequency between the wave signals of the firstpair and the wave signals of the second pair.

41. Wave signal receiving apparatus Acomprising means to receive aplurality of pairs of signals radiated from at least two separatelocations with at least one signal having modulated thereon referencesignals derived from beating the signals of a first of said pairs ofsignals, said pairs of signals being ofdistinguishably dierentfrequencies with the two signals forming each pair being radiated fromdifferenti-locations and with each pair of signals having the samefrequency separation, said receiving apparatus including means forreproducing the reference signals, for heterodyning the signals of thefirst pair to produce a first beat frequency and for Iheterodyning thesignals of a second of said pairs to produce a second beat frequencysignal equal in frequency to the first beat frequency signal, meansjointly responsive to the reproduced reference signals and to the firstbeat frequency signal for producing a first position irtdication relatedto the frequencies of the signals of the first pair, and means jointlyresponsive to said first and second beat frequency signals to provide aposition indication related to vthe frequency difference between saidpairs.

42. In a position determining system, a pair of continuous wave systemsof the type transmitting wave signals from separate transmitters andproviding beat frequency signals for use in developing reference signalsfor transmission, said systems operating at different frequencies,receiver means for each of said systems for receiving said diyerentfrequency signals, means responsive to the outputs of the receiver meansfor providing a yrst position indication related to the frequencies ofthe wave signals of one of said systems, and means responsive to theoutputs of said receiver means for providing a second positionindication relatefd to the frequency dierence bet1fveen the wave signalsof said pair of systems.

43. A system for providing position indications, comprising rst andsecond continuous wave transmission systems each including spacednon-synchronized transmitters for continuously transmitting wave signalsfrom separate points arid receiving means responsive to the wave signalsradiated by both of said systems for providing position indicationsrelated to the relative values of the frequencies of said first andsecond systems.

44. A system for providing position indications, comprising first andsecond continuous wave transmission systems each including spacednon-synchronized transmitters for continuously transmitting wave signalsfromI separate points and receiving means responsive to the wave signalsradiated by both of said systems for providing position indications interms of the frequency difference between the wave signals of the firstand second systems.

4References Cited in the le of this patent or the original patent IUNITED STATES PATENTS Re. 23,050

